DESCRIPTION OF THE SPECIES OF PTERYGOTUS 257 
Of the carapace or eyes we have yet no trace. But the efzstoma 
(fig. 1) presents us with a singularly neat character for the species. 
The upper portion of this organ is broadly sagittate or spear-shaped, 
as in other species, and offers a wider basal angle than that of 
P. anglicus, but the outer portion, which is quite straight and linear, 
(instead of being clavate,) is bilobed at the tip; and from the deep 
terminal notch a raised central line is continued nearly all the way 
up the linear portion, and terminating in a slight prominence. The 
whole piece is smooth. 
Of the first dody ring a fragment an inch and a half long and 
one inch wide is figured (Plate X. [Plate 21] fig. 2). It is the 
semi-circular sweep of the outer edge of the segment, where it fits 
into the scooped out portion of the succeeding (second) one. The 
rounded margin a is serrated, the serrations pointing backward. The 
sculpture is very minute, prominent, and confined to the forward 
half, except a few marginal plicae on the hinder edge. All are longer 
than wide. Fig. 2@ shows them magnified. Fig. 3 is without much 
doubt the second thoracic segment. It is wider at the sides than in 
the middle, and turns up abruptly at the forward angle to form the 
characteristic process. Fig. 4 appears to be a larger specimen of 
the third ring, it has the same characters of ornamentation. In 
both the central portion is less arched than in P. anuglicus or 
P. arcuatus, and the sides less oblique and minutely crenulate. 
A narrow (articular?) furrow runs along the middle portion of the 
anterior edge, followed by a convex ridge, which is bounded by a 
row of prominent minute tubercles extending a good way out, and 
nearly to the lateral margins. Behind this the anterior third of 
the segment is occupied by the sculpture, which is much more pro- 
minent and tubercular, and less scale-like than in the large Scotch 
species. 
The occurrence of this line of tubercles enables us to connect 
with the species some very curious fragments, one of which is here 
figured (fig. 8) with one or other of the body rings. When first 
viewed the piece appears quite anomalous, the extended ends giving 
the general form much the aspect of the epistoma, but a closer 
examination shows that it has an upper surface 6, and the impression 
of the lower side c, each with the sculpture pointing backwards, 
and with no room for a median lobe. Of the eprstoma we have 
now obtained specimens (fig. 1, as above described), and it remains 
therefore to explain this piece as one of the body rings, obliquely 
pressed, (probably the exuviated crust only,) the angular edge being 
indicated at a, and one surface (the inferior) ¢, being less disturbed 
VOL. Il, 5 
